This invention relates to the art of producing honeycomb structures from extrudable material such as particulate ceramic and/or metal batches and similar materials which have the property of being able to flow or plastically deform during extrusion, while being able to become sufficiently rigid immediately thereafter so as to maintain their structural integrity. More particularly, the present invention relates to an improved extrusion die assembly for forming a honeycomb structure having differing cell structures including differing geometries and/or cellular densities, across the width or face of the extruded honeycomb structure, while simultaneously providing an inner skin between the differing cells.
The prior art has suggested the use of various cell geometries in a cellular substrate; however, such art does not disclose the applicant's method of producing such structures or does it contemplate the unique concerns of the extrusion die apparatus of the present invention.
U.S. Pat. No. 3,853,485 relates to a core member for a catalytic oxidation converter, wherein the cross-sectional area of the cells or passages through the core member increase progressively from a central one of a plurality of patterns of passages toward the next concentric pattern of passages.
U.S. Pat. No. 4,168,944 relates to a complex apparatus for manufacturing a tubular honeycomb assembly with an adiabatic layer formed integrally on the peripheral wall thereof.
U.S. Pat. No. 4,448,828 relates to ceramic honeycomb structural bodies having flexible cells in the center to provide good thermal stress absorption, while outer rigid cells provide high mechanical strength. The patent relates to the structural body only, and not as to how it is formed.
U.S. Pat. No. 4,810,554 relates to a high strength ceramic honeycomb structure having triangular outer cells which improve the isostatic strength of square inner cells. Again, the patent relates to the cell shape, and not to the manufacture of such shape.
In order to overcome the problems and complexities of the above noted prior art, it is an object of the present invention to set forth a simple and relatively inexpensive method for providing an appropriate apparatus to produce an extruded article having multi-cellular densities and/or multi-cellular geometries.